1. Field of the Invention
This invention relates to photographic couplers and silver halide photographic materials, in particular to yellow dye-forming couplers useful in silver halide photographic materials, and more particularly to a class of yellow couplers known as acylacetanilides having an electron withdrawing group attached to the keto-functional group, and to their use in silver halide color photographic light-sensitive elements, emulsions, and to processes using such couplers.
2. Description of Related Art
The subtractive process of color formation is customarily employed in multi-colored photographic elements. The resulting yellow, magenta, and cyan image dyes are formed in silver halide layers sensitive to blue, green, and red radiation, respectively.
It is well known in the photographic art that these color images are customarily obtained by a coupling reaction between an oxidized aromatic primary amine developer and a color-forming coupler. It is important that the dye formed from the color-forming couplers have the proper light absorption characteristics. Thus, ideally, the yellow dye should have a high absorption for blue radiation and no or very low absorption for green and red radiation.
Typically, yellow dye-forming couplers are open-chain ketomethylene compounds which yield azomethine dyes upon coupling with oxidized developers. The most common yellow dye-forming couplers are acylacetanilides such as pivaloylacetanilides and benzoylacetanilides. Representative couplers of these classes are described in U.S. Pat. Nos. 2,298,443; 2,407,210; 2,875,057; 3,048,194; 3,265,506; 3,447,928; 4,157,919; 4,230,851; 4,327,175; 4,401,752; and 4,529,691. Furthermore, "Farbkupplereine Literaturubersicht" published in Agfa Mittelunger, Band II, pp 112-126 (1961) describes such couplers.
Furthermore, U.S. Pat. No. 3,056,675 describes benzoyl acetanilide couplers of the formula: ##STR1## wherein X is a halogen. These benzoylacetanilide type couplers are not within the scope of the couplers of the present invention because "X" is not on a carbon adjacent to the carbonyl.
These known yellow dye-forming couplers frequently used in the photographic art often do not possess the absorption characteristics discussed above to the desired extent. In particular, they absorb not only blue light, but often undesirable quantities of green and red light. For instance, some of the known yellow-dye forming couplers are orange-colored because they have unwanted absorption in the green and the red portion of the spectrum. Furthermore, pivaloylacetanilide yellow couplers of the structure ##STR2## have in general low coupler efficiency due to their high pKa value and benzoylacetanilide yellow couplers of the structure ##STR3## form yellow image dyes with very poor light fastness.
Accordingly, there has been a need to find yellow-dye forming couplers which improve upon existing couplers and optimize photographic properties such as the light absorption characteristics discussed above. In particular, it would be highly desirable to develop a yellow-dye forming coupler which substantially absorbs only blue light, with minimal or no absorption of green and red light.
There is further a need to provide a silver halide color photographic element containing yellow dye-forming couplers having these beneficial light absorption characteristics and to provide a process of using such an element.